Author Topic: Strange Noise on Transmit  (Read 1543 times)

wb7ely

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Strange Noise on Transmit
« on: 2017-05-15, 05:53:57 »
Running an IC-706 and AT-4 to a 40 ft long wire + RRC on an internal network. The antenna is 35 ft horizontally from the radio and RRC. Monitoring my transmitted signal on another receiver, I hear this horrible buzzing noise. Checked grounding and power supply, all good. Running the RRC and 706 on the same 20A Astron xfmr power supply. I thought I saw a post where it was suggested that the two units be run from separate 12V supplies, anyone have experience with this? Tried to attach an mp4 audio file of the buzzing noise, but appears it is not one of the accepted file types..

Dave
WB7ELY
//Dave WB7ELY

sm2o

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Re: Strange Noise on Transmit
« Reply #1 on: 2017-05-15, 10:28:48 »
Hi
With unbalanced antennas i suspect you suffer from RFI. Try to reduce the output power to a minimum to find out if it's RFI. If so you need to prevent RF to flow back into the schack by RF Chokes etc. Separate PS may reduce GND loops but the main issue is to keep RF out of the schack

73 de mike

wb7ely

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Re: Strange Noise on Transmit
« Reply #2 on: 2017-05-16, 04:09:41 »
Mike-- Thanks for your inputs. I am thinking it is not the antenna. I am using an Icom auto-tuner 35 ft from the radio and RRC. The tuner is tuning the wire antenna just like it should. I am unable to change anything by reducing the power. Its like motorboating as soon as I go to transmit. Any wisdom on grounding the RRC? Any suggestions on separating the RRC 12V power from the radio power?

//Dave WB7ELY

VK3ALB

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Re: Strange Noise on Transmit
« Reply #3 on: 2017-05-16, 05:52:10 »
Dave,

I assume your receiver is nearby? Has anyone far away (a few miles) confirmed this sound you are hearing? Could it simply be RX overload or RF getting in to the RX where it shouldn't be? How is the RX powered?

You might have a grounding problem with RRC but as Mike suggested it is more likely an antenna issue. There are loads of people out there that use one supply for the rig end (radio and RRC) and one supply for the control end (head and RRC) without any issue. Also, I'm probably not the first person to run everything (2 x RRC, rig and control head) from a single power supply when setting up and testing a new configuration. My take on that is that RRC is pretty immune to problems of ground loops etc.

Could you try to put a dummy load in place of the tuner at the end of the 35ft of coax (checks the cable too) then see what happens?

If the buzzing goes away you have some work to do on your antenna/tuner system because RF is probably getting in to the rest of your gear. If the buzzing is still there you should start a process of elimination that may include supplying the rig RRC from a battery - just to see if it helps.

Lou
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wb7ely

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Re: Strange Noise on Transmit
« Reply #4 on: 2017-05-18, 03:52:52 »
Lou--Thanks for your ideas. The buzzing transmitted signal was verified by monitoring on a receiver about .5 mile away and was also confirmed by a ham about 1500 miles south of me in Sacramento. I wired the remote RRC on a separate supply today (12V marine battery) and I get three dual tone beeps on the control RRC and the remote will apparently not power up. It had a power light. Tomorrow I will take my heath "cantenna" to the remote radio and try that.
I am running a fairly odd configuration. There is a 900 ft private mountain behind my QTH and I have access to it and an outlet! The outlet is about 100+ ft from the radio due to the wifi link. So I am running a small line of sight wifi link to the mountain and then running the RRC and IC706. Wow! what a difference in HF signal strengths! But nothing is easy and this issue has me puzzling. Here's a link to some photos: http://www.valhallatreefarm.com/WB7ELY/RRC/rrc.htm

73 Dave
WB7ELY
//Dave WB7ELY

sm2o

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Re: Strange Noise on Transmit
« Reply #5 on: 2017-05-18, 08:10:11 »
Check the extension cable and the red straps also, it can be a screen  or a red strap which is broken.

73 de mike

VK3ALB

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Re: Strange Noise on Transmit
« Reply #6 on: 2017-05-19, 00:59:27 »
I wired the remote RRC on a separate supply today (12V marine battery) and I get three dual tone beeps on the control RRC and the remote will apparently not power up. It had a power light.

Strange. If all you did was disconnect the RRC power and install the battery then the system should still power up. Something wrong there. If you want to pursue the idea of separate supplies you need to find out why adding the battery did not work.
Lou
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wb7ely

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Re: Strange Noise on Transmit
« Reply #7 on: 2017-05-19, 05:22:12 »
Thanks guys, looks like that was a red herring. The three beeps, I now know, tell me that the link is not connecting. Verified that the wifi link to the mtn behind the QTH is inoperative.As soon as I get that going, I will be back on the track.

73 de WB7ELY
//Dave WB7ELY

Jerry1920123

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Re: Strange Noise on Transmit
« Reply #8 on: 2017-06-13, 04:46:16 »
Dave, I connected a dummy load to the radio this eliminated the buzzing sound. Inspecting my antenna with a analyzer found the antenna has major problems. To be sure my feed line was good I connected the dummy load to the feed line disconnecting the antenna, no more buzzing.  High SWR back into the shack is my problem hope his helps.

wb7ely

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Re: Strange Noise on Transmit
« Reply #9 on: 2017-06-13, 05:46:19 »
Thanks all for your inputs
I have tried a dummy load connected to the antenna and still l have a hum on the transmitted audio
I think Mike nailed it with his suggestion to go over the Icom 706 separation cable and splices to the RJ45 connectors
But I have redone the splices three times with particular attention to the mike audio and shield. (no help!)
I have shortened the radio side cable to the bare minimum of 12" and shortened the RJ45 pigtail to 3" (no help!)
The modified cable works fine (no hum) when connected through a "double female" RJ45 connector and run the radio.
So I am about to give up and sell the 706 and buy a TS480.
Any further suggestions would be greatfully accepted.

De Dave WB7ELY
//Dave WB7ELY

sm2o

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Re: Strange Noise on Transmit
« Reply #10 on: 2017-06-13, 07:43:50 »
The Remoterig system was orginally designed for IC-706. IC-706 was also during long time the most popular rig to use with Remoterig. If there is no bad solderings in the cables, and the mic and mice straps is OK it must be something else from outside which cause the hum. RFI is probably the most usual, bad power supply or ground loops can also be a reason. but check the MICE straps again to be sure they are not broken

73 de mike

Jerry1920123

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Re: Strange Noise on Transmit
« Reply #11 on: 2017-06-13, 15:22:43 »
Dave, I had to ohm out the jumper wire connections from the control and radio to the RJ45 connector to verify they where correct then made sure the mic ground and chassis ground where correct. I hope this helps. I have been in commercial radio communications since 1982 still working but close to retirement.
I have RF going into my RRC and plan to purchase a intelligent tuner at the base of my antenna to reduce RF on the LMR 600.  . Also have shielded Ethernet cable to use on the mic to radio. It seems the RRC is very perceptible to RF interference.
Amateur radio is fun to experiment with don't give up.